Multistage Extension and Age Dating of the Xiaoqinling Metamorphic Core Complex,Central China   总被引：2，自引：0，他引：2  

ZHANG Jinjiang 《《地质学报》英文版》1999,73(2):139-147

There are two extensional systems in the Xiaoqinling metamorphic core complex (XMCC). One is the detachment fault system developed along the peripheries of the XMCC, which extended in an ESE-WNW direction and whose upper plate moved towards the WNW. The other extensional system includes the retrograde shear zones and normal faults developed within the XMCC, which represent the collapse of the XMCC. Ar-Ar and K-Ar dating shows that the extension of the detachment fault system continued from 135 to 123 Ma, i.e. in the late stage of its evolution at about 127 Ma. The collapse represented by the extensional system within the XMCC was operative during 120(106 Ma, and its main activity occurred about 116 Ma ago. These suggest that the XMCC experienced two extensional stages in its evolution, i.e., the syn-orogenic regional extension and post-orogenic collapse extension.  相似文献   

阿尔泰南缘托库孜巴依金矿床流体包裹体特征及成矿流体演化     

张敏  牛向龙  莫凌超  牛斯达  吴华英  周起凤 《岩石学报》2020,36(4):1171-1185

新疆西北部的托库孜巴依(巴依)金矿床位于西伯利亚古板块南缘,阿尔泰陆缘活动带克兰弧后盆地与哈巴河弧间盆地接壤处。本次研究在前人成果基础上,通过详细的野外调查、室内显微观察、流体包裹体测温、激光拉曼成分分析和氢-氧同位素分析等多种方法,揭示了巴依金矿各成矿阶段流体特征、成矿热液来源和流体演化过程。根据野外矿脉空间分布、穿插关系、矿物组合及结构构造等特征,结合流体包裹体研究,本文将巴依金矿的成矿作用划分为4个阶段:石英-磁铁矿阶段(Ⅰ),主要发育富液相包裹体,均一温度范围在3529～4134℃区间,盐度范围为73%～147%NaCleqv,平均为104%NaCleqv;石英-黄铁矿阶段(Ⅱ),该阶段主要发育富液相包裹体、富气相包裹体以及含子晶包裹体,均一温度范围为1860～3398℃,盐度变化范围为27%～443%NaCleqv,平均为92%NaCleqv;石英-黄铁矿-黄铜矿阶段(Ⅲ)主要发育富液相包裹体和含(富)CO_2三相水溶液包裹体,均一温度范围为1410～1864℃(富液相包裹体),盐度范围较大,介于0～88%NaCleqv之间;石英-方解石阶段(Ⅳ),流体包裹体以富液相为主,均一温度范围1020～1400℃,盐度范围为02%～43%NaCleqv。该矿床从成矿早阶段到成矿晚阶段温度-盐度整体呈下降趋势,在主要成矿阶段(Ⅱ、Ⅲ)出现流体沸腾现象。各成矿阶段δ~(18)O、δD同位素变化范围分别为:成矿早阶段(Ⅰ)531‰和-8510‰;主要成矿阶段(Ⅱ、Ⅲ)-153‰～150‰和-974‰～-811‰;成矿晚阶段(Ⅳ)-352‰～-342‰和-939‰～-871‰,成矿流体主要是早阶段的变质水与中晚阶段加入的大气水混合而成。巴依金矿成矿流体表现为一套中低盐度NaCl-H_2O-CO_2流体体系,符合造山型金矿成矿流体特征。综合矿床地质研究,本文认为在晚石炭世-二叠纪喀拉通克岛弧与西伯利亚板块碰撞造山构造体制下,流体混合、压力降低和沸腾作用是巴依金矿床富集成矿的主要机制。  相似文献   

Pitfalls in the AMS radiocarbon-dating of terrestrial macrofossils     

B. Wohlfarth  G. Skog  G. Possnert  B. Holmquist 《第四纪科学杂志》1998,13(2):137-145

The AMS ¹⁴C technique has the advantage that small samples of Late Quaternary age can be dated with high accuracy, and that errors due to reservoir effects can be avoided if specifically determined terrestrial micro- and macrofossils are measured. However, to obtain such high-accuracy measurements, it is important how small samples are handled prior to treatment in the radiocarbon laboratories. Here we present a set of 51 AMS ¹⁴C measurements, of which 31 dates gave expected ages and 20 dates resulted in anomalously young ages, despite the fact that all samples consisted of clearly identified Late Weichselian terrestrial plant macrofossils. To evaluate possible sources of error, we compared these samples in respect to preparation methods, sample storage and sample weight. Our results show that the long-term storage of wet macrofossil samples appears to have a significant effect on the radiocarbon age obtained, even when the samples are kept cool. Fungi or micro-organisms may easily be incorporated into a sample during preparation and identification, and can easily contribute to the contamination of a sample, if stored cool and wet for several months. © 1998 John Wiley & Sons, Ltd.  相似文献   

新疆哈尔里克山口门子韧性剪切带变形期次及年代学研究     

查雁鸿  王国灿  申添毅  曹同礼  张攀 《大地构造与成矿学》2020,(2):297-310

新疆哈尔里克山口门子韧性剪切带作为东天山地区重要的构造记录之一,其变形期次及年代学研究对认识博格达?哈尔里克山乃至整个东天山的区域构造演化具有重要意义。本文基于宏观与微观变形特征、变形温压条件、同位素年代学研究,厘定了两期(脆)?韧性变形,分别是早期韧性逆冲变形和晚期左旋脆?韧性走滑变形。卷入早期韧性逆冲变形的花岗岩、火山岩年代学分析表明,该期变形发生于440.1±3.2 Ma之后;未卷入该期变形的花岗闪长岩脉和辉绿岩脉年代学分析表明,早期韧性逆冲变形发生于298.1±1.0 Ma之前。结合泥盆纪?早石炭世哈尔里克山地区呈现为稳定构造环境以及存在早、晚石炭世地层间的角度不整合,推断早期韧性逆冲变形形成于早、晚石炭世之交,与石炭纪陆内裂谷的闭合有关。晚期左旋脆?韧性走滑变形叠加使早期糜棱岩面理发生褶皱,结合前人获得的259±1 Ma的变质绢云母^40Ar-^39Ar年龄,认为该期变形是晚二叠世受西伯利亚板块向南推挤的陆内转换压缩变形产物。  相似文献   

斑岩钼-热液脉状铅锌银矿成矿系统特征、控制因素及勘查指示   总被引：1，自引：0，他引：1  

金露英  秦克章  李光明  赵俊兴  李真真 《岩石学报》2020,36(12):3813-3839

斑岩钼矿与热液脉状铅锌银矿为两类重要的矿床类型,两者往往分别独立产出,但越来越来的勘查实例揭示二者也可共生产出,构成统一的成矿系统。斑岩钼-热液脉状铅锌银成矿系统,主要分布在北美西部、加拿大西南部、中国秦岭-大别地区、华北北缘及西拉沐伦带、大兴安岭北段-额尔古纳等地区。根据斑岩钼矿与热液脉状铅锌银矿的平面关系,成矿系统可分为近源和远源两类：近源时,两者直接叠置或者平面距离小于2km;而远源时,两类矿化平面距离一般不超过6km。成矿系统空间上表现可为上铅-锌-银、下钼的垂向叠置或者内钼、外铅-锌-银侧向共存的形式。时间上两类矿化一般近同期形成,或者相差通常不超过8Myr。成矿系统岩浆性质多为高演化的钙碱性花岗质岩浆,起源于下地壳且加入了不同比例的地幔物质。成矿系统的蚀变特征一般为斑岩钼矿化蚀变向热液脉状铅锌银矿蚀变的渐变,其中粘土化带与绢英岩化带是两类矿床的叠加区。钼矿化常与钾硅酸盐化或者绢英岩化带内侧密切相关,铅锌银矿化则常与浅部的低温硅化-绢云母-伊利石-水白云母化、碳酸盐化密切相关。基于S、Pb、Sr、Nd等同位素研究成果,钼铅锌银系统中成矿物质主要为岩浆来源,但可能有地层物质的加入。成矿流体主要以岩浆水来源为主,初始流体通常为单相中低密度流体,辉钼矿沉淀往往伴随着减压沸腾、大气水混合、冷却及/或水岩反应的进行,发生大规模钼矿化的温度区间通常在300~450℃。浅部脉状铅锌银矿化则由持续降温的流体在混入较多大气水或流体pH值中和而形成,温度区间在175~320℃。成矿系统空间上钼-铅-锌-银的分带,可能受控于流体演化过程中上述多个过程的综合叠加作用。通过总结对比钼铅锌银成矿系统、单一斑岩钼矿、单一热液脉状铅锌银矿床在勘查历史、构造因素、成矿岩体属性、流体特征、特征矿物、地球物理-地球化学勘查指标等方面的异同,本文提出了指示浅部热液脉状铅锌银矿之下同一成矿系统深部斑岩钼矿的找矿标志,且对该成矿系统形成的岩浆性质、岩浆-热液系统、成矿元素、构造条件、保存条件等多个方面进行了探讨。在前人基础上,本文提出本类成矿系统理论研究展望：1）利用微区原位技术分辨矿物的不同期次及元素的分布状态,进而获得该类型铅锌银矿相对准确的成矿年龄;2）确定斑岩钼-热液脉状铅锌银成矿系统的初始流体成矿元素和相关配位剂元素的含量;3）建立钼铅锌银成矿系统的矿物学指示标志;4）查明成矿系统岩浆过程、元素行为等精细成矿过程,研究其与其他成矿系统的差异。上述问题的深入研究和找矿标志的提出或将提高对斑岩钼-脉状铅锌银成矿系统成矿过程的认识,为该类系统勘查找矿工作提供理论支撑。  相似文献   

Geochemistry and zircon U-Pb ages of the Oligocene sediments in the Baiyun Sag,Zhujiang River Mouth Basin     

Rui Sun  Ming Ma  Kai Zhong  Xiayang Wang  Zhao Zhao  Shuai Guo  Xingzong Yao  Gongcheng Zhang 《海洋学报(英文版)》2021,40(2):123-135

In this study, element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin. The experimental results are discussed with respect to weathering conditions, parent rock lithologies, and provenances. The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering. Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements, "V"-shaped negative Eu anomalies, and negligible Ce anomalies. The rare earth element distribution curves are obviously right-inclined, with shapes and contents similar to those of post-Archean Australian shale and upper continental crust, indicating that the samples originated from acid rocks in the upper crust. The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area. For the samples from the upper Enping deltas, the overall age spectrum shows four major age peaks ca. 59–68 Ma, 98–136 Ma, 153–168 Ma and 239–260 Ma. For the Zhuhai Formation samples,the overall age spectrum shows three major age peaks ca. 149 Ma, 252 Ma and 380 Ma. The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation, the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances: Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift, and the former supply became stronger through time. Thus, the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.  相似文献   

The Mineralization of the Beiya Skarn Gold Deposit in Yunnan, Southwest China     

HE Wenyan  YU Xuehui  DONG Guochen  HUANG Xiongfei 《《地质学报》英文版》2013,87(Z1):692-693

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Inversion of provenance data and sediment load into spatially varying erosion rates     

Fien De Doncker  Frédéric Herman  Matthew Fox 《地球表面变化过程与地形》2020,45(15):3879-3901

Sediment fingerprinting methods aim to determine the relative contribution of different source areas in detrital sediments based on natural properties – fingerprints – of the source areas. Here, we use U/Th–Pb age signatures as fingerprints, assuming that the age signal is not altered during erosion–transportation–deposition events, and given that recent technological advances enable precise dating of large amounts of grains. We introduce a formal inversion method that allows to disentangle the amalgamation of source contributions in detrital zircon data and enables to convert this information into an erosion rate map starting from the spatial distribution of zircon age signatures. Relying on the least-squares method and using prior and covariance information to deal with non-uniqueness, we show, using synthetic and natural examples, that we are able to retrieve erosion rate patterns of a catchment when the age distribution and zircon fertility for each source area are well known. Moreover, we show that not only zircon age fingerprints but also other tracers such as mineral content can be used. Furthermore, we found that adding data from samples taken at the outlet of tributaries improves the estimation of erosion rate patterns. We conclude that the least squares inverse model applied to detrital data has great potential for investigating erosion rates. © 2020 John Wiley & Sons, Ltd.  相似文献   

东昆仑西段阿确墩地区白沙河岩组锆石U-Pb年龄 ——对前寒武纪基底演化的约束     

李猛  查显锋  胡朝斌  高晓峰  李婷  姚志亮 《地质通报》2021,(1):41-57

对东昆仑西段阿确墩地区金水口岩群白沙河岩组片麻岩进行了LA-ICP-MS锆石U-Pb年代学研究.结果显示,片麻岩中锆石的年龄范围为2400～410 Ma,峰值范围为1650～1400 Ma,其中存在少量新元古代(1.0～0.9 Ga)和早古生代(410 Ma)的变质锆石,从而限定了原岩的最早沉积时代,为中元古代末期,指...  相似文献   

Late Triassic initial closure of the Mongol-Okhotsk Ocean in the western segment: Constraints from sedimentological,detrital zircon ages and paleomagnetic evidence     

《Gondwana Research》2024

The Mesozoic evolution of the Mongol-Okhotsk Ocean (MOO) has significantly affected the configuration of the modern Asian continent. Although a scissor-like closure of the MOO has long been proposed, when and how the MOO closed are still hotly debated, especially the timing of initial closure of the MOO in its western segment, hindering our understanding of both the evolution of the MOO and tectonics of the northern Asian continent. In order to uncover the timing of initial closure of the MOO, we performed a multidisciplinary study in sedimentology, detrital zircon U-Pb dating and paleomagnetic on the Late Triassic clastic strata from the Tarvagatay Block and the Amuria Block (AMB) on the both sides of the Mongol-Okhotsk Suture. The upper Triassic strata on both sides of the suture were dominated by plant fossil-bearing alluvial-fluvial facies sediments, which unconformably overlain pre-Triassic geological units, indicating a terrestrial setting after the closure of the MOO. Detrital zircon U-Pb dating results revealed consistent age distribution patterns for samples from both sides of the suture with a predominant peak at ∼253–251 Ma and a secondary peak at ∼359–357 Ma, representing two main arc magmatic events during the bidirectional subduction of the MOO in the Late Devonian-Early Carboniferous and Late Permian-Early Triassic. Coeval Late Triassic paleomagnetic poles were obtained from the northern AMB and Tarvagatay Block, revealing a comparable paleolatitude of the AMB (∼31–33°) and Tarvagatay Block (∼32–34°) in the Late Triassic, arguing for that the western segment of the MOO should have closed at the Late Triassic. The compilation of sedimentology, detrital zircon U-Pb dating, magmatic and paleomagnetic evidence provides integrated constraints on the Late Triassic initial closure of the MOO in its western segment.  相似文献